In the main people disbelieve because they choose to disbelieve, because they love something else, usually a sin, more than God and wish to continue in the rebellion against God, and the biggest rebellion against God is to disacknowledge Him entirely by unbelief.
Why did God make Satan or angels capable of falling? A precursor probably to human redemption. Angels are from the beginning supposed to minister to the heirs of salvation. Human believers will judge angels. If Satan was made fallible, it was also for our good.
When it says “all things work together for good to them that love God, to those that are called according to his promises” I take it literally.
Even what Satan determines for our ill becomes good, just as Joseph said to his brothers that they intended him harm, but God intended it for good.
Do you think I should share these explanations with a broader public on HTV?